Generally, semiconductor devices include a plurality of circuits that form an integrated circuit (IC) fabricated on a semiconductor substrate. A complex network of signal paths will normally be routed to connect the circuit elements distributed on the surface of the substrate. Efficient routing of these signals across the device requires formation of multilevel or multilayered schemes, such as, for example, single or dual damascene wiring structures. The wiring structure typically includes copper, Cu, or a Cu alloy since Cu-based interconnects provide higher speed signal transmission between large numbers of transistors on a complex semiconductor chip as compared with aluminum, Al-based interconnects.
Within a typical interconnect structure, metal vias run perpendicular to the semiconductor substrate and metal lines run parallel to the semiconductor substrate. Further enhancement of the signal speed and reduction of signals in adjacent metal lines (known as “crosstalk”) are achieved in today's IC product chips by embedding the metal lines and metal vias (e.g., conductive features) in a dielectric material having a dielectric constant of less than 4.0.
In current semiconductor interconnect structures, time-dependent-dielectric-breakdown (TDDB) has been identified as one of the major reliability concerns for future interconnect structures that include Cu-based metallurgy and low k dielectric materials. By “TDDB” it is meant that overtime the dielectric material of the interconnect structure begins to fail. The failure of the dielectric material may be caused by intrinsic means or by defects that are formed on the surface of the interconnect dielectric material during the course of preparing the interconnect structure.
Leakage of metallic ions, particularly Cu ions, along the interconnect dielectric surface has been identified as the major intrinsic failure mechanism that attributes to TDDB. FIG. 1 is a prior art interconnect structure 10 which illustrates this intrinsic leakage phenomenon. Specifically, the prior art interconnect structure includes a dielectric material 12 having a Cu feature 14 embedded therein. The Cu feature 14 is typically separated from the dielectric material 12 by a diffusion barrier 16. A dielectric capping layer 18 is present on the surface of the dielectric material 12, the diffusion barrier 16 and the Cu feature 14. In FIG. 1, arrows 20 designate the leakage (diffusion) of Cu ions from the conductive feature 14 which occurs along the upper surface of the interconnect structure as shown. Overtime this leakage of Cu ions results in TDDB as well as failure of the devices within the interconnect structure. In addition to arrows 20, FIG. 1 also includes curved arrows 21 which represent the direction of the electrical field that is generated between neighboring conductive features embedded within the dielectric material of the interconnect structure.
Another contributor to TDDB, which is also illustrated in FIG. 1, is defect related. Specifically, Cu residues (e.g., defects) 22 are present at the interface between the upper surface of the dielectric material 12 and the dielectric capping layer 18. The Cu residues 22 are formed during the formation of the Cu features 14 (i.e., deposition and planarization of Cu within an opening formed into the dielectric material 12). Post planarization Cu residues, which provide defects at the surface of the dielectric material, are one of the root causes of time-dependent-dielectric-breakdown (TDDB) failure.
It is observed that although Cu is specifically mentioned with respect to the prior art interconnect structures mentioned above, the above leakage and defect problems occur (although at different rates and extents) with other types of conductive metals such as, for example Al and W. It is further observed that the dielectric breakdown failure reliability related concern described above, is getting worse as integrated circuit critical dimensions continue to scale down.
In view of the above, there is a need for providing an interconnect structure in which the dielectric breakdown failure reliability related concern mentioned above is reduced or even completed eliminated.